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Passing sentence Judge Michael told Henry: "I have no doubt you are dangerous," adding "there is a significant risk to members of the public."

"On September 15, 2011, you were given a suspended sentence order by Lincoln Magistrates for harrasment of Miss Boswell. You were released from the custody of the court and made a silent phonecall to Miss Boswell," Judge Heath said.

"You then made a phonecall to Miss Boswell on a mobile phone and told her 'I'm out.' I am satisfied both of those calls were to frighten her."

Judge Heath described Henry's account that he stabbed Miss Boswell by accident as "nonsense."

"This incident followed several years of you making Miss Boswell's life a misery."

Miss Boswell, a mother of three, had been harassed by Henry for three or four years before he stabbed her.

The jury was told Miss Boswell retreated into her daughter's bedroom after Henry used a plant pot to break in. But Henry clambered over the bed towards Miss Boswell with a knife taken from her kitchen, and thrust that knife to the right side of her chest.

Henry had been to Miss Boswell's home the previous weekend and climbed onto her roof before saying he intended to kill her. He was arrested on 14 September for breaching a restraining order which had been made to prevent him harassing Miss Boswell, and appeared before magistrates in Lincoln the following day.

Henry was given an eight-week sentence but this was suspended.

After leaving court he retrieved some possessions from a police station in West Parade, Lincoln, and telephoned Miss Boswell from a call box opposite the station.

"She answered, but the caller, this defendant, remained silent," Robert Underwood, prosecuting, said.

"A little later he rang Claire Boswell again. He was using a mobile phone. When she answered that call this defendant said to her 'I'm out'."

Jurors heard Mr Henry went to Miss Boswell's house in Glentham Road, Gainsborough, at about 5.15 the same day after taking a train from Lincoln.

When interviewed by police, he admitted breaking into her house and getting a knife from her kitchen, but said he just intended to sit down and talk to her.

"He went into the bedroom where Claire Boswell was. She was pressing an alarm button that the authorities had provided for her on an earlier occasion."

Miss Boswell then dialled 999 and was heard shouting during the call: "Help! Get out!"

"Mr Henry was simply not deterred," said Mr Underwood.

"He clambered over the bed towards Claire Boswell, knife still in hand, and he thrust that knife to the right side of her chest."

The wound penetrated her breast tissue and injured her liver, causing her life threatening injuries. She suffered a pierced liver and was taken to Lincoln Hospital, then transferred to Queen’s Medical Centre in Nottingham where she remained for five days.

Miss Boswell had called the police to complain about Henry on "around 40 occasions" since 2005, the jury heard.

Giving evidence from behind a screen during the trial Miss Boswell said: "I complained when I got fed up and could not cope anymore," adding, "normally I ring the police when I am frightened."

Henry, of Lea Place, Gainsborough, later told police: "I didn't want to kill her or 'owt like that.

The jury were told Henry had a string of previous convictions for violence, including grievous bodily harm, assault and using a knife to cut the fingers of a male relative of his then girlfriend.

Henry was told he must serve of mininum of nine years imprisonment before he is considered for parole.